Transit advocates are ramping up their efforts to convince Mayor Bill de Blasio to subsidize half-fare MetroCards by urging New Yorkers to fill up his inbox and voicemail.

Riders Alliance and the Community Service Society of New York launched the weeklong “Call the Mayor” effort on the corner of 125th Street and St. Nicholas Avenue in Harlem on Monday, even offering phones for riders to use.

“City Council Speaker Corey Johnson supports Fair Fares, now we need Mayor Bill de Blasio to get on board as well,” said Rebecca Bailin of the Riders Alliance.

Bailin said half-priced MetroCards would help 800,000 New Yorkers who live at or below the federal poverty line. She pointed out senior citizens, students and people with disabilities already receive discounts.

“New Yorkers can’t wait for a tax from Albany that may or may not come through,” she said.

De Blasio has said the money should come from his proposed millionaire’s tax that would need to be approved by the state legislature.

The City Council included $212 million to pay for the cards in its budget response. But the program was not part of de Blasio’s $89 billion Fiscal Year 2019 executive budget.

“The Mayor supports Fair Fares,” Seth Stein, a spokesman for de Blasio, said in a statement. “But instead of making riders and low-income New Yorkers pay the bill for it, he believes a tax on millionaires should fund the fare discount.”

After a brief news conference, staffers from Riders Alliance and the Community Service Society fanned out across the block and down into the subway to pass out information cards.

“They want to raise the fares again,” said Alexis Palmer, a student at Parsons School of Design. “Disadvantaged and poor people can’t afford that. Even middle class people can’t afford that.”

Nikeea Thomas, who lives in Harlem and works in security for a real estate company, said sometimes she struggles to pay for MetroCards for herself and her three sons — one of whom is a college student.